1. Field of the Invention
The present invention relates to a bent state holding mechanism of an endoscope.
2. Description of the Related Art
In typical endoscopes, a bendable portion control mechanism for bending the bendable portion, which is provided in the vicinity of the distal end of the insertion portion of the endoscope, by remote control is freely rotatably mounted to the control portion that is coupled to the proximal end of the insertion portion of the endoscope, and such endoscopes are provided with a bent state holding mechanism for holding the bendable portion control mechanism at any given rotation position by exerting frictional resistance on the rotating operation of the bendable portion control mechanism so that the free end of the insertion portion of the endoscope remains directed toward a target affected area, or the like.
The bent state holding mechanism of such conventional endoscopes is provided with frictional resistance producing members which exert frictional resistance on the rotating operation of the bendable portion control mechanism. Such frictional resistance producing members are made from a doughnut-shaped frictional disk made of a soft material such as rubber or cork and a metal disk which is pressed against the entire surface of the frictional disk on one side thereof. This structure is disclosed in, e.g., Japanese patent publications H09-98942 and Japanese patent publication 2005-160791.
However, if such a frictional disk that is made of a soft material such as rubber or cork is used as one frictional resistance producing member of the bent state holding mechanism, a second metal disk or the like needs to be provided on the back of the frictional disk to support the frictional disk; moreover, a disk spring or the like needs to be provided or the frictional disk of a soft material needs to be formed to have a sufficient thickness.
Consequently, the bent state holding mechanism of the conventional endoscope becomes great in thickness, which increases the size of a bendable portion control knob of the endoscope if the bent state holding mechanism is installed in an internal space of the bendable portion control knob to thereby deteriorate the operability thereof, and which sometimes makes it difficult for another mechanism (e.g., a torque limiting mechanism for preventing a torque exerted on the bendable portion control knob from being transmitted to the bendable portion for safety when the torque exceeds a predetermined torque) to be installed in an internal space of the bendable portion control knob if so desired.
In addition, the frictional disk made of rubber, cork or the like cannot be formed in a precise flat shape, which causes only a radially outer portion or a radially inner portion of the frictional disk to be pressed against the metal disk, and accordingly, the magnitude of the frictional resistance which occurs by pressure contact of the frictional disk with the metal disk varies greatly.
Additionally, the frictional disk made of rubber, cork or the like is vulnerable to heat and easy to deteriorate with time, so that a prescribed magnitude of frictional resistance may not be obtained over a long period of time if high-temperature steam under pressure sterilization is repeated after each use of the endoscope.
Additionally, in the bent state holding mechanism of the endoscope, the operability of the endoscope is enhanced if the bendable portion can be bent simply by performing a bendable portion control operation (i.e., without requiring to perform an operation releasing the application of frictional resistance to the rotating operation of the bendable portion control mechanism) after the bendable portion control mechanism has been stopped and held at any given rotational position by a frictional resistance exerted on the rotating operation of the bendable portion control mechanism by the bent state holding mechanism and if the bendable portion control mechanism can be stopped and held at another rotation position once this bending portion control operation is stopped. However, since dynamic friction of rubber, cork, or the like, is unstable and often becomes greater than static friction thereof, the bendable portion becomes very heavy when it is operated unless the application of frictional resistance is released in conventional bent state holding mechanisms, which deteriorates the operability of the endoscope.